FFmpeg
dsd.c
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1 /*
2  * Direct Stream Digital (DSD) decoder
3  * based on BSD licensed dsd2pcm by Sebastian Gesemann
4  * Copyright (c) 2009, 2011 Sebastian Gesemann. All rights reserved.
5  * Copyright (c) 2014 Peter Ross
6  *
7  * This file is part of FFmpeg.
8  *
9  * FFmpeg is free software; you can redistribute it and/or
10  * modify it under the terms of the GNU Lesser General Public
11  * License as published by the Free Software Foundation; either
12  * version 2.1 of the License, or (at your option) any later version.
13  *
14  * FFmpeg is distributed in the hope that it will be useful,
15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17  * Lesser General Public License for more details.
18  *
19  * You should have received a copy of the GNU Lesser General Public
20  * License along with FFmpeg; if not, write to the Free Software
21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
22  */
23 
24 #include <string.h>
25 #include "libavutil/attributes.h"
26 #include "libavutil/reverse.h"
27 #include "libavutil/thread.h"
28 #include "dsd.h"
29 
30 #define CTABLES ((HTAPS + 7) / 8) /** number of "8 MACs" lookup tables */
31 
32 /*
33  * Properties of this 96-tap lowpass filter when applied on a signal
34  * with sampling rate of 44100*64 Hz:
35  *
36  * () has a delay of 17 microseconds.
37  *
38  * () flat response up to 48 kHz
39  *
40  * () if you downsample afterwards by a factor of 8, the
41  * spectrum below 70 kHz is practically alias-free.
42  *
43  * () stopband rejection is about 160 dB
44  *
45  * The coefficient tables ("ctables") take only 6 Kibi Bytes and
46  * should fit into a modern processor's fast cache.
47  */
48 
49 /**
50  * The 2nd half (48 coeffs) of a 96-tap symmetric lowpass filter
51  */
52 static const double htaps[HTAPS] = {
53  0.09950731974056658, 0.09562845727714668, 0.08819647126516944,
54  0.07782552527068175, 0.06534876523171299, 0.05172629311427257,
55  0.0379429484910187, 0.02490921351762261, 0.0133774746265897,
56  0.003883043418804416, -0.003284703416210726, -0.008080250212687497,
57  -0.01067241812471033, -0.01139427235000863, -0.0106813877974587,
58  -0.009007905078766049, -0.006828859761015335, -0.004535184322001496,
59  -0.002425035959059578, -0.0006922187080790708, 0.0005700762133516592,
60  0.001353838005269448, 0.001713709169690937, 0.001742046839472948,
61  0.001545601648013235, 0.001226696225277855, 0.0008704322683580222,
62  0.0005381636200535649, 0.000266446345425276, 7.002968738383528e-05,
63  -5.279407053811266e-05, -0.0001140625650874684, -0.0001304796361231895,
64  -0.0001189970287491285, -9.396247155265073e-05, -6.577634378272832e-05,
65  -4.07492895872535e-05, -2.17407957554587e-05, -9.163058931391722e-06,
66  -2.017460145032201e-06, 1.249721855219005e-06, 2.166655190537392e-06,
67  1.930520892991082e-06, 1.319400334374195e-06, 7.410039764949091e-07,
68  3.423230509967409e-07, 1.244182214744588e-07, 3.130441005359396e-08
69 };
70 
71 static float ctables[CTABLES][256];
72 
73 static av_cold void dsd_ctables_tableinit(void)
74 {
75  int t, e, m, sign;
76  double acc[CTABLES];
77  for (e = 0; e < 256; ++e) {
78  memset(acc, 0, sizeof(acc));
79  for (m = 0; m < 8; ++m) {
80  sign = (((e >> (7 - m)) & 1) * 2 - 1);
81  for (t = 0; t < CTABLES; ++t)
82  acc[t] += sign * htaps[t * 8 + m];
83  }
84  for (t = 0; t < CTABLES; ++t)
85  ctables[CTABLES - 1 - t][e] = acc[t];
86  }
87 }
88 
90 {
91  static AVOnce init_static_once = AV_ONCE_INIT;
92  ff_thread_once(&init_static_once, dsd_ctables_tableinit);
93 }
94 
95 void ff_dsd2pcm_translate(DSDContext* s, size_t samples, int lsbf,
96  const uint8_t *src, ptrdiff_t src_stride,
97  float *dst, ptrdiff_t dst_stride)
98 {
99  uint8_t buf[FIFOSIZE];
100  unsigned pos, i;
101  uint8_t* p;
102  double sum;
103 
104  pos = s->pos;
105 
106  memcpy(buf, s->buf, sizeof(buf));
107 
108  while (samples-- > 0) {
109  buf[pos] = lsbf ? ff_reverse[*src] : *src;
110  src += src_stride;
111 
112  p = buf + ((pos - CTABLES) & FIFOMASK);
113  *p = ff_reverse[*p];
114 
115  sum = 0.0;
116  for (i = 0; i < CTABLES; i++) {
117  uint8_t a = buf[(pos - i) & FIFOMASK];
118  uint8_t b = buf[(pos - (CTABLES*2 - 1) + i) & FIFOMASK];
119  sum += ctables[i][a] + ctables[i][b];
120  }
121 
122  *dst = (float)sum;
123  dst += dst_stride;
124 
125  pos = (pos + 1) & FIFOMASK;
126  }
127 
128  s->pos = pos;
129  memcpy(s->buf, buf, sizeof(buf));
130 }
acc
int acc
Definition: yuv2rgb.c:554
ctables
static float ctables[CTABLES][256]
Definition: dsd.c:71
thread.h
b
#define b
Definition: input.c:40
ff_reverse
const uint8_t ff_reverse[256]
Definition: reverse.c:23
reverse.h
dsd.h
CTABLES
#define CTABLES
Definition: dsd.c:30
FIFOMASK
#define FIFOMASK
Definition: dsd.h:32
ff_thread_once
static int ff_thread_once(char *control, void(*routine)(void))
Definition: thread.h:175
av_cold
#define av_cold
Definition: attributes.h:90
s
#define s(width, name)
Definition: cbs_vp9.c:257
htaps
static const double htaps[HTAPS]
The 2nd half (48 coeffs) of a 96-tap symmetric lowpass filter.
Definition: dsd.c:52
AV_ONCE_INIT
#define AV_ONCE_INIT
Definition: thread.h:173
src
#define src
Definition: vp8dsp.c:255
AVOnce
#define AVOnce
Definition: thread.h:172
ff_init_dsd_data
av_cold void ff_init_dsd_data(void)
Definition: dsd.c:89
HTAPS
#define HTAPS
Definition: dsd.h:30
a
The reader does not expect b to be semantically here and if the code is changed by maybe adding a a division or other the signedness will almost certainly be mistaken To avoid this confusion a new type was SUINT is the C unsigned type but it holds a signed int to use the same example SUINT a
Definition: undefined.txt:41
attributes.h
i
int i
Definition: input.c:406
dsd_ctables_tableinit
static av_cold void dsd_ctables_tableinit(void)
Definition: dsd.c:73
DSDContext
Per-channel buffer.
Definition: dsd.h:41
ff_dsd2pcm_translate
void ff_dsd2pcm_translate(DSDContext *s, size_t samples, int lsbf, const uint8_t *src, ptrdiff_t src_stride, float *dst, ptrdiff_t dst_stride)
Definition: dsd.c:95
pos
unsigned int pos
Definition: spdifenc.c:412
samples
Filter the word “frame” indicates either a video frame or a group of audio samples
Definition: filter_design.txt:8
FIFOSIZE
#define FIFOSIZE
Definition: dsd.h:31